Engine Harmonic Enhancement Control

ABSTRACT

In a general aspect, a system includes a controller configured to receive a first signal representative of a load on an engine and to generate a control parameter based on the first signal, one or more harmonic scaling elements, each configured to receive the control parameter and a different engine harmonic signal of a plurality of engine harmonic signals and to generate a scaled version of the received engine harmonic signal. Each, harmonic scaling element includes a harmonic specific mapping element for mapping the control parameter to a harmonic specific scaling factor, wherein at least some of the harmonic specific scaling factor values of the harmonic specific mapping element are mapped to control parameter values which are associated with a negative load on the engine, and an adjustable gain element for forming a scaled version of the received engine harmonic signal including applying the harmonic specific scaling factor to the received engine harmonic signal. The controller is further configured to condition the first signal to remove transient components before generating the control parameter.

PRIORITY CLAIM

This application is a continuation of U.S. patent application Ser. No.15/874,583, filed Jan. 18, 2018, which is a continuation of U.S. patentapplication Ser. No. 14/874,749, filed Oct. 5, 2015, which is acontinuation of U.S. patent application Ser. No. 13/437,092, filed Apr.2, 2012, the entire contents of which are incorporated here byreference.

BACKGROUND

This specification relates to engine harmonic enhancement.

In some situations, automobile operators find it desirable to hear thenoise emanating from the engine of their automobile. For example, adriver of a sports car may want to hear engine noise as they accelerate.The operator may use the noise to determine when to shift gears or theymay just find that engine noise enriches their driving experience.

However, many modern day automobiles are designed to reduce the amountof noise (e.g., road noise) that enters the automobile's cabin andreaches the operator. To achieve noise reduction, automobile designersoften insulate the automobile's cabin with sound dampening materials(e.g., foam). The sound dampening materials do not discriminate betweenengine noise and other noise such as road noise. Therefore, the use ofsound dampening materials tends to attenuate the amount of engine noisethat reaches the operator. Furthermore, in some examples, the sounddampening materials attenuate certain frequencies of the engine noisemore than others, resulting in an unnatural sounding engine noisereaching the operator.

Engine harmonic enhancement systems enhance the engine noise heard bythe operator by playing a synthesized engine noise through the audiosystem in the cabin of the automobile.

SUMMARY

In a general aspect, a system includes a controller configured toreceive a first signal representative of a load on an engine and togenerate a control parameter based on the first signal, one or moreharmonic scaling elements, each configured to receive the controlparameter and a different engine harmonic signal of a plurality ofengine harmonic signals and to generate a scaled version of the receivedengine harmonic signal. Each, harmonic scaling element includes aharmonic specific mapping element for mapping the control parameter to aharmonic specific scaling factor, wherein at least some of the harmonicspecific scaling factor values of the harmonic specific mapping elementare mapped to control parameter values which are associated with anegative load on the engine, and an adjustable gain element for forminga scaled version of the received engine harmonic signal includingapplying the harmonic specific scaling factor to the received engineharmonic signal.

Aspects may include one or more of the following features.

The controller may be further configured to receive a second signalrepresentative of a throttle position and wherein the controller isfurther configured to generate the control parameter based on both thefirst signal and the second signal. At least some of the harmonicspecific scaling factors of the harmonic specific mapping element may bemapped to control parameters which are associated with a positive loadon the engine. The control parameters which are associated with thenegative load on the engine may be derived from the first signal and thecontrol parameters which are associated with the positive load on theengine may be derived from the second signal.

The controller may be further configured condition the first signal toremove transient components before generating the control parameter. Thecontroller may be further configured to apply a scale factor to thefirst signal such that values of the first signal which are greater thana first threshold map to a linear range. The linear range may extendfrom 0% to 100%. The controller may be further configured to apply afirst scale factor to the first signal such that negative values of thefirst signal map to a first linear range, and apply a second scalefactor to the second signal such that all values of the second signalmap to a second linear range. The first linear range may extend from−100% to 0% and the second linear range may extend from 0% to 100%. Thefirst signal may include a torque signal.

In another general aspect, a method includes receiving a plurality ofengine harmonic signals, receiving a first signal representative of aload on an engine, determining a control parameter based on the firstsignal, determining a harmonic specific scaling factor for each of oneor more engine harmonic signals of the plurality of engine harmonicsignals, and applying the corresponding harmonic specific scaling factorto each of the one or more engine harmonic signals. Determining theharmonic specific scaling factor includes, for each of the one or moreengine harmonic signals, providing the control parameter to acorresponding harmonic specific mapping function configured to mapcontrol parameter values to harmonic specific scaling factor valueswherein at least some of the harmonic specific scaling factor values aremapped to control parameter values which are associated with a negativeload on the engine.

Aspects may include one or more of the following features.

The method may include receiving a second signal representative of athrottle position and wherein determining the control parameter is basedon both the first signal and the second signal. At least some of theharmonic specific scaling factors may be mapped to control parameterswhich are associated with a positive load on the engine. The controlparameters which are associated with the negative load on the engine maybe derived from the first signal and the control parameters which areassociated with the positive load on the engine may be derived from thesecond signal. Determining the control parameter based on the firstsignal may include conditioning the first signal to remove transientcomponents. Determining the control parameter may include applying ascale factor to the first signal such that values of the first signalwhich are greater than a first threshold map to a linear range. Thelinear range may extend from 0% to 100%.

Determining the control parameter may include applying a first scalefactor to the first signal such that negative values of the first signalmap to a first linear range; and applying a second scale factor to thesecond signal such that all values of the second signal map to a secondlinear range. The first linear range may extend from −100% to 0% and thesecond linear range may extend from 0% to 100%. The first signal mayinclude a torque signal.

In a general aspect, a system includes a controller configured toreceive a first signal representative of a load on an engine and togenerate a control parameter based on the first signal and one or moreharmonic scaling elements. Each of the one or more harmonic scalingelements is configured to receive the control parameter and a differentengine harmonic signal of a plurality of engine harmonic signals and togenerate a scaled version of the received engine harmonic signal. Eachharmonic scaling element includes a harmonic specific mapping elementfor mapping the control parameter to a harmonic specific scaling factorand an adjustable gain element for forming a scaled version of thereceived engine harmonic signal including applying the harmonic specificscaling factor to the received engine harmonic signal.

In another aspect, a method includes receiving a plurality of engineharmonic signals, receiving a first signal representative of a load onan engine, determining a control parameter based on the first signal,determining a harmonic specific scaling factor for each of one or moreengine harmonic signals of the plurality of engine harmonic signals andapplying the corresponding harmonic specific scaling factor to each ofthe one or more engine harmonic signals. Determining the harmonicspecific scaling factor including, for each of the one or more engineharmonic signals, providing the control parameter to a correspondingharmonic specific mapping function configured to map control parametervalues to harmonic specific scaling factor values; and

Embodiments of the invention may have one or more of the followingadvantages.

Using a signal representative of an engine load to scale individualengine harmonics allows embodiments to generate one type of engine noisefor positive engine loads and another type of engine noise for negativeengine loads. This feature makes the result of the engine harmonicenhancement system sound more realistic than the result of conventionalengine harmonic enhancement systems.

Using a signal representative of an engine load to scale individualengine harmonics enables the system to continuously change the harmonicstructure of engine noise as engine load changes.

Other features and advantages of the invention are apparent from thefollowing description, and from the claims.

DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram of a first engine harmonic enhancement (EHE)system.

FIG. 2 is a block diagram of a first EHE controller.

FIG. 3 is a first mapping element.

FIG. 4 is a block diagram of a second EHE system.

FIG. 5 is a block diagram of a second EHE controller.

FIG. 6 is a second mapping element.

FIG. 7 is a graph illustrating blipping.

FIG. 8 is a block diagram of a third EHE controller.

FIG. 9 is a block diagram of a third EHE system.

DESCRIPTION 1 System Overview

Referring to FIG. 1, an engine harmonic enhancement system 100 receivesa torque signal 102 representative of a torque output of an engine (notshown) and an RPM signal 104 representative of a number of revolutionsper minute of the engine as input signals. The system 100 uses the inputsignals 102,104 to form a combined engine harmonic signal 108 which isprovided to an automobile audio system 106 for presentation to anautomobile operator (not shown).

The engine harmonic enhancement system 100 includes a harmonicsgenerator 112, an engine harmonic scaling module 114, and a summer 116.The RPM signal 104 is first provided to the harmonics generator 112which generates a number of individual engine harmonics 119 based on theRPM signal 104. In some examples, the harmonics generator 112 includes alookup table (LUT) which associates values of the RPM signal 104 withfundamental frequency values. The first harmonic (H₁) generated by theharmonics generator 112 is the fundamental frequency which correspondsto the value of the RPM signal 104. The remaining engine harmonics 119(H₂-H_(N)) are generated at harmonic frequencies of the fundamentalfrequency.

The torque signal 102 and the engine harmonics (H₁-H_(N)) 119 generatedby the harmonics generator 112 are provided to the engine harmonicscaling module 114 which generates a scaled version 130 of each of theengine harmonics 119 based on the torque signal 102. The torque signal102 is especially useful for determining scaling factors for each of theengine harmonics 119 since it includes information relating not only theamount of load on the engine but also relating to whether the engineload is positive or negative. This information can be used, for example,to generate one type of engine noise when the automobile is acceleratingand another type of engine noise when the automobile is decelerating dueto engine braking.

The engine harmonic scaling module 114 includes an engine harmonicenhancement (EHE) controller 115 and a number of engine harmonic scalingelements 120. The EHE controller 115 receives the torque signal 102 anddetermines a control parameter, (P) 122, based on the torque signal 102.A number of embodiments of the EHE controller 115 are described indetail in later sections of this specification.

The EHE controller 115 provides the control parameter 122 to each of theengine harmonic scaling elements 120. Each engine harmonic scalingelement 120 also receives one of the engine harmonics 119 generated bythe harmonics generator 112. Each engine harmonic scaling element 120scales the received engine harmonic 119 based on the control parameter122.

To perform scaling of an individual engine harmonic 119, each engineharmonic scaling element 120 includes a mapping element 126 and anadjustable gain element 128. The mapping element 126 receives thecontrol parameter 122 and uses it to determine a harmonic scaling value124. In some examples, the mapping element 126 is a lookup table whichincludes a number of harmonic scaling values 124 which are associatedwith a corresponding control parameter 122 value. In other examples, themapping element implements a mathematical function which receives thecontrol parameter 122 as an input and calculates the harmonic scalingvalue 124. In some examples, each of the mapping elements 126 implementsa different mapping between the control parameter 122 and the harmonicscaling values 124 depending on which engine harmonic 119 is beingscaled by the engine harmonic scaling element 120 in which the mappingelement 126 is included.

The received engine harmonic 119 and the harmonic scaling value 124 areprovided to the adjustable scaling element 128 which applies theharmonic scaling value 124 to the received engine harmonic 119,resulting in the scaled engine harmonic signal 130.

Each of the scaled engine harmonic signals 130 generated by the harmonicscaling elements 120 is provided to a summer 116 which adds the scaledengine harmonic signals 130, resulting in the combined engine harmonicsignal 108.

2 Torque Based EHE Controller

Referring to FIG. 2, one embodiment of the EHE controller 115 receivesthe torque signal 102 and generates the control parameter, (P) 122,based on the torque signal 102. The EHE controller 215 includes a torquesignal interpreter 232, a torque value calibrator 238 and a parameterdetermination module 234.

The torque signal interpreter 232 receives the torque signal 102 which,in some examples, is a digital signal representing a physical torquevalue with units of Ngn (i.e., Newton gmeters). The torque signalinterpreter 132 transforms the digital torque signal 102 into itscorresponding physical torque value 236 and provides the physical torquevalue 236 to the torque value calibrator 238.

The torque value calibrator 238 forms a calibrated torque value 240 bymapping the entire range of possible physical torque values 236 to aneasy to use range of values. In general, a given physical torque values236 represented by the torque signal 102 can be either positive ornegative. For example, if the automobile engine is causing theautomobile to accelerate (i.e., a positive engine load), the physicaltorque value 236 is positive. If the automobile engine is engaged to theautomobile drive train and the automobile is decelerating (i.e., enginebraking causing a negative engine load), the physical torque value 236is negative. Furthermore, in some examples, the maximum positivephysical torque value is different than the maximum negative physicaltorque value.

The mapping performed by the torque value calibrator 238 is illustratedby the following example. In this example, the range of possiblephysical torque values 236 for one exemplary vehicle may be −80 Nm to400 Nm. The torque signal calibrator 238 scales the physical torquevalue 236 in such a way that physical torque values 236 in the range of0 Nm to 400 Nm are mapped to a range of 0% to 100%. This is accomplishedby multiplying the physical torque value 236 by a scale factor of 0.25.Similarly, physical torque values 236 in the range of −80 Nm to 0 Nm aremultiplied by the 0.25 scale factor, thereby mapping these torque valuesto a range of −20% to 0%. Thus, for this example, the calibrated torquevalue 240 output from the torque value calibrator 238 falls within arange of −20% to 100%.

The calibrated torque value 240 is then provided to a control parameterdetermination module 234. In this embodiment, the control parameterdetermination module 234 simply uses the calibrated torque value as thecontrol parameter, (P) 122. As is described above, the control parameter122 is provided to the mapping elements (FIG. 1, element 126) includedin the engine harmonic scaling elements (FIG. 1, element 120).

3 Mapping Element

Referring to FIG. 3, one example of a mapping element 326 receives thecontrol parameter 122 which was generated by the EHE controller 115 ofFIG. 3 and uses the control parameter 122 to determine a harmonicscaling value 124. In particular, the value of the control parameter 122is found on the x-axis (which ranges from −20% to 100% as in the exampledescribed above) and the value of the harmonic gain curve 342 at thecontrol parameter 122 value is output as the harmonic scaling value 124.

Note that the harmonic scaling curve 342 is asymmetric about theharmonic gain axis (i.e., the y-axis). This asymmetry accounts forsituations where an individual harmonic level in an engine noisegenerated by an engine experiencing a positive engine load (i.e., whileaccelerating) is different than an individual harmonic level in anengine noise generated by an engine experiencing a negative engine load(i.e., while engine braking).

Referring to FIG. 4, another embodiment of an engine harmonicenhancement system 400 is configured in much the same way as the engineharmonic enhancement system 100 of FIG. 1 but is further configured toaccept a throttle signal 403 which the EHE controller 415 uses inconjunction with the torque signal 102 to determine the controlparameter, (P) 422. In some examples, the throttle signal 403 representsa percentage of throttle opening.

4 Torque and Throttle Based EHE Controller

Referring to FIG. 5, the EHE controller 415 of in FIG. 4 is configuredto accept the torque signal 102 and the throttle signal 403 as signalinputs and to use the signal inputs 102, 403 to determine the controlparameter, (P) 422. In general, for positive engine loads, the EHEcontroller 415 is configured to use a throttle percentage value 545 asthe control parameter 422. For negative engine loads, the EHE controller415 is configured to use a calibrated torque signal 540 as the controlparameter 422.

The EHE controller 415 includes a torque signal interpreter 232, atorque value calibrator 538, a throttle signal interpreter 544, and acontrol parameter determination module 534.

The throttle signal interpreter 544 receives the throttle signal 403which, in some examples, is a digital signal representing a percentageof throttle opening in the range of 0% to 100%. The throttle signalinterpreter 132 transforms the digital throttle signal 403 into itscorresponding throttle percentage value 545. In some examples, thethrottle percentage value 545 is already in the form of a percentagewith a range of 0% to 100% and therefore does not need to be calibrated.In other examples, a scaling factor of 1.0 can be applied to thethrottle percentage value 545 to preserve its range of values.

The torque signal interpreter 232 interprets the torque signal 102 inthe same as way as the torque signal interpreter 232 of FIG. 2,generating a physical torque value 236. The physical torque value 236 ispassed to the torque value calibrator 538 which scales the physicaltorque value 236 such that negative physical torque values 236 aremapped to a range of −100% to 0% (or −1 to 0). For example, the range ofphysical torque values 236 for one exemplary vehicle may be −100 Nm to400 Nm. The torque signal calibrator 538 scales the physical torquevalues 236 in such a way that physical torque values 236 in the range of−100 Nm to 0 Nm are mapped to a range of −100% to 0%. In this example,this can be accomplished by multiplying the physical torque value 236 bya scale factor of 1.25.

The throttle percentage value 544 and the calibrated torque value 540are provided to the control parameter determination module 534 whichuses the values 544, 540 to determine the control parameter, (P) 422. Inparticular, if the throttle percentage value 544 is greater than apredetermined throttle threshold, A0, OR if the calibrated torque value540 is greater than a predetermined torque threshold, T0, the throttlepercentage value output as the control parameter 422. Otherwise, thecalibrated torque value 540 is output as the control parameter 422. Insome examples, the threshold values T0 and A0 are equal to zero. Inother examples, the threshold values T0 and A0 are values close to zero.

The resulting control parameter 422 output from the EHE controller 415is bounded to a range of −100% to 100%. When the engine load isnegative, the control parameter 422 includes a calibrated torque value540 within the range of −100% to 0% and when the engine load ispositive, the control parameter includes a throttle percentage value 544within the range of 0% to 100%.

5 Combined Torque and Throttle Based Mapping Element

Referring to FIG. 6, another example of a mapping element 426 receivesthe control parameter 422 which was generated by the EHE controller 415of FIG. 4 and uses the control parameter 422 to determine a harmonicscaling value 424. In particular, the value of the control parameter 422is found on the x-axis (which ranges from −100% to 100% as in theexample described above) and the value of the harmonic gain curve 642 atthe control parameter 422 value is provided as the harmonic scalingvalue 424 output.

Again, note that the harmonic scaling curve 642 is asymmetric about theharmonic gain axis (i.e., the y-axis). This asymmetry accounts forsituations where an individual harmonic level in an engine noisegenerated by an engine experiencing a positive engine load (i.e., whileaccelerating) is different than an individual harmonic level in anengine noise generated by an engine experiencing a negative engine load(i.e., while engine braking). Also note that the control parameter 422values from −100% to 0% are based on negative torque values 536 and thecontrol parameter values 422 from 0% to 100% are based on positivethrottle percentage values 545.

5 Blipping Resistant EHE Controller

Referring to FIG. 7, in some examples, during engine braking anautomobile may shift from a higher gear to a lower gear (i.e.,downshift). In order to shift gears, a clutch which couples an engine ofthe automobile to a drive train of the automobile is disengaged at whichtime the RPMs of the automobile engine decrease to an idling level whilethe drive train of the automobile continues to rotate at a high rate.Re-engaging the clutch at the lower gear while the engine is rotating atthe idling level can cause an abrupt and undesirable decrease in speedas the quickly rotating drive train couples to the more slowly rotatingengine.

To avoid this abrupt decrease in speed, the engine RPMs can be increasedsuch that the engine is rotating at a rate which is comparable that ofthe drive train, a technique referred to as ‘RPM Matching.’ Thisincrease in engine RPMs prior to engaging the clutch is also sometimesreferred to as ‘blipping.’

The circled areas 746 in FIG. 7 illustrate the torque output of anautomobile engine during engine braking. The spike in torque 748 betweenthe two circles illustrates the torque of the engine as the automobiledownshifts and blipping occurs. This type of spike 748 in the torquesignal can have a detrimental effect on EHE systems which utilize torqueinformation (e.g., the systems described above). In particular, such aspike can cause the EHE system to generate a loud and undesirable enginenoise for a very short time. In some examples, the loud engine noise isan engine noise associated with engine acceleration and not with enginebraking, as would be expected.

Referring to FIG. 8, another embodiment of an EHE controller 815 isconfigured to generate the control parameter 822 in a way that lessensthe effect of blipping on EHE systems which utilize torque information.The EHE controller 815 operates similarly to the EHE controller 415illustrated in FIG. 5. However, before being provided to the torquevalue calibrator 538, the physical torque value 236 is first provided toan absolute value element 850 which generates the absolute value 851 ofthe physical torque value 236. The absolute value 851 of the physicaltorque value 236 is provided to a negation module 852 which generates anegated absolute value 853 of the physical torque value 236. The negatedabsolute value 853 of the physical torque value 236 is then provided toa coercion module 854 which coerces the negated absolute value 853 ofthe physical torque value 236 to a predetermined range. In someexamples, the predetermined range is defined as the range which includesall possible torque values between a maximum torque output of theautomobile engine and a minimum torque output of the automobile engine.

The coerced negated absolute value 855 is provided to the torque valuecalibrator 538 which scales the coerced negated absolute value 855 ofthe physical torque value 236 such that negative values of the coercednegated absolute value 855 of the physical torque signal 236 are mappedto a range of −100% to 0% (or 0 to 1). The output of the torque valuecalibrator 538 is a calibrated torque value 840 which is provided to thecontrol parameter determination module 834 along with the throttlepercentage value 544. If the throttle percentage value 544 is greaterthan a predetermined threshold, A0, the throttle percentage value 545 isoutput as the control parameter 822. Otherwise the calibrated torquevalue 840, which is conditioned such that effects of blipping areminimized, is output as the control parameter 822.

7 Alternatives

Referring to FIG. 9, in some examples, each of the engine harmonicscaling elements 920 of the engine harmonic enhancement system 900includes a smoothing element 960 which receives the harmonic scalingvalue 424 generated by the mapping element 426 and uses it to generateat smoothed harmonic scaling value 924.

In some examples, the smoothing element 960 generates the smoothedharmonic scaling value 925 by applying an attack and decay algorithm.Such an algorithm causes abrupt changes in the harmonic scaling value tobe represented more gradually in the harmonic scaling value 924.

In some examples, the torque signal 102 and the throttle signal 403 arereceived from a controller area network (CAN) bus.

8 Implementations

Systems that implement the techniques described above can be implementedin software, in firmware, in digital electronic circuitry, or incomputer hardware, or in combinations of them. The system can include acomputer program product tangibly embodied in a machine-readable storagedevice for execution by a programmable processor, and method steps canbe performed by a programmable processor executing a program ofinstructions to perform functions by operating on input data andgenerating output. The system can be implemented in one or more computerprograms that are executable on a programmable system including at leastone programmable processor coupled to receive data and instructionsfrom, and to transmit data and instructions to, a data storage system,at least one input device, and at least one output device. Each computerprogram can be implemented in a high-level procedural or object-orientedprogramming language, or in assembly or machine language if desired; andin any case, the language can be a compiled or interpreted language.Suitable processors include, by way of example, both general and specialpurpose microprocessors. Generally, a processor will receiveinstructions and data from a read-only memory and/or a random accessmemory. Generally, a computer will include one or more mass storagedevices for storing data files; such devices include magnetic disks,such as internal hard disks and removable disks; magneto-optical disks;and optical disks. Storage devices suitable for tangibly embodyingcomputer program instructions and data include all forms of non-volatilememory, including by way of example semiconductor memory devices, suchas EPROM, EEPROM, and flash memory devices; magnetic disks such asinternal hard disks and removable disks; magneto-optical disks; andCD-ROM disks. Any of the foregoing can be supplemented by, orincorporated in, ASICs (application-specific integrated circuits).

It is to be understood that the foregoing description is intended toillustrate and not to limit the scope of the invention, which is definedby the scope of the appended claims. Other embodiments are within thescope of the following claims.

1. A system for engine harmonic enhancement, comprising: a controllerconfigured to receive a first signal representative of a load on anengine and to generate a control parameter based on the first signal;one or more harmonic scaling elements, each configured to receive thecontrol parameter and a different engine harmonic signal of a pluralityof engine harmonic signals and to generate a scaled version of thereceived engine harmonic signal, each harmonic scaling elementincluding: a harmonic specific mapping element for mapping the controlparameter to a harmonic specific scaling factor, wherein at least someof the harmonic specific scaling factor values of the harmonic specificmapping element are mapped to control parameter values which areassociated with a negative load on the engine; and an adjustable gainelement for forming a scaled version of the received engine harmonicsignal including applying the harmonic specific scaling factor to thereceived engine harmonic signal, wherein the controller is furtherconfigured condition the first signal to remove transient componentsbefore generating the control parameter.
 2. The system of claim 1wherein the controller is further configured to receive a second signalrepresentative of a throttle position and wherein the controller isfurther configured to generate the control parameter based on both thefirst signal and the second signal.
 3. The system of claim 2 wherein atleast some of the harmonic specific scaling factors of the harmonicspecific mapping element are mapped to control parameters which areassociated with a positive load on the engine.
 4. The system of claim 3wherein the control parameters which are associated with the negativeload on the engine are derived from the first signal and the controlparameters which are associated with the positive load on the engine arederived from the second signal.
 5. The system of claim 1 wherein thecontroller is further configured to apply a scale factor to the firstsignal such that values of the first signal which are greater than afirst threshold map to a linear range.
 6. The system of claim 5 whereinthe linear range extends from 0% to 100%.
 7. The system of claim 3wherein the controller is further configured to apply a first scalefactor to the first signal such that negative values of the first signalmap to a first linear range; and apply a second scale factor to thesecond signal such that all values of the second signal map to a secondlinear range.
 8. The system of claim 7 wherein the first linear rangeextends from −100% to 0% and the second linear range extends from 0% to100%.
 9. The system of claim 1 wherein the first signal includes atorque signal.
 10. A method of engine harmonic enhancement, comprising:receiving a plurality of engine harmonic signals; receiving a firstsignal representative of a load on an engine; determining a controlparameter based on the first signal; determining a harmonic specificscaling factor for each of one or more engine harmonic signals of theplurality of engine harmonic signals including, for each of the one ormore engine harmonic signals, providing the control parameter to acorresponding harmonic specific mapping function configured to mapcontrol parameter values to harmonic specific scaling factor values;wherein at least some of the harmonic specific scaling factor values aremapped to control parameter values which are associated with a negativeload on the engine; and applying the corresponding harmonic specificscaling factor to each of the one or more engine harmonic signals,wherein determining the control parameter based on the first signalincludes conditioning the first signal to remove transient components.11. The method of claim 10 further comprising receiving a second signalrepresentative of a throttle position and wherein determining thecontrol parameter is based on both the first signal and the secondsignal.
 12. The method of claim 11 wherein at least some of the harmonicspecific scaling factors are mapped to control parameters which areassociated with a positive load on the engine.
 13. The method of claim12 wherein the control parameters which are associated with the negativeload on the engine are derived from the first signal and the controlparameters which are associated with the positive load on the engine arederived from the second signal
 14. The method of claim 10 whereindetermining the control parameter includes applying a scale factor tothe first signal such that values of the first signal which are greaterthan a first threshold map to a linear range.
 15. The method of claim 14wherein the linear range extends from 0% to 100%.
 16. The method ofclaim 12 wherein determining the control parameter includes: applying afirst scale factor to the first signal such that negative values of thefirst signal map to a first linear range; and applying a second scalefactor to the second signal such that all values of the second signalmap to a second linear range.
 17. The method of claim 16 wherein thefirst linear range extends from −100% to 0% and the second linear rangeextends from 0% to 100%.
 18. The method of claim 10 wherein the firstsignal includes a torque signal.